I think the problem is in the path. As other people mention above in the css code it should be written:
I use this in my PRS-650 for embedded fonts and it works fine.
Alternatively, sometimes instead of embedding the fonts in the ePub file I create a folder called 'Fonts' in the root of the internal memory of the reader and save the fonts there. Then the syntax used in the css is:
And don't forget that css is case sensitive!
I hope it will help.